This invention relates generally to the field of air conditioning. More particularly the invention relates to an apparatus for both heating and cooling an enclosed space with an air source closed loop vapor compression refrigeration system.
Air source vapor compression refrigeration systems have long been used both to cool and heat enclosed spaces. Such systems that both heat and cool are commonly called heat pumps. The principles of operation of heat pumps are well known. In an air source system, air is the source of heat for evaporating refrigerant in the system evaporator and also the heat sink for condensing refrigerant in the system condenser. When it is desired to cool the space, air is drawn from the space, caused to flow though the system evaporator where it is cooled, and then returned to the space. When it is desired to heat the space, air is drawn from the space, caused to flow through the system condenser where it is heated, and then returned to the space. In an air source system, air from outside the enclosed space is the source of heat for heating and the heat sink for cooling.
Shifting a heat pump between cooling and heating modes may be accomplished in one of two ways. One way is to keep the air flow paths the same and to reverse the flow of refrigerant through the inside and outside heat exchangers so that they trade functions on a mode change, that is, the inside heat exchanger, the evaporator during operation in the cooling mode, becomes the condenser during operation in the heating mode while the outside heat exchanger similarly changes functions. Another way to shift modes is to shift air flows. In a system using this method, the refrigerant flow is the same in both modes with one heat exchanger thus functioning as the evaporator and the other as the condenser for both heating and cooling. The air flow paths shift on a mode change so that inside air flows through the evaporator during operation in the cooling mode and through the condenser during operating in the heating mode while outside air flow similarly shifts between heat exchangers.
There are some disadvantages to mode shifting by reversing system refrigerant flow. First, a flow reversing valve is necessary. Second, there must be either an additional expansion device or there must be another device that is capable of causing refrigerant expansion in both directions of refrigerant flow. Third, a heat exchanger in a flow reversing system must be capable of functioning as both a condenser and an evaporator. The configuration of such a heat exchanger must necessarily be a compromise between the differing designs for an optimal condenser and an optimal evaporator. All these factors may result in increased cost for such a reversible system. In addition, the flow reversing valve may be a source of noise when it repositions when shitting modes.
There are numerous examples in the prior art of vapor compression heat pump systems in which the mode shift from cooling to heating is accomplished by shifting air flows. Among these are U.S. Pat. No. 1,942,296, issued 2 Jan. 1934 to Kerr et al., U.S. Pat. No. 2,216,427, issued 1 Oct. 1940 to Arnold et al., U.S. Pat. No. 2.293,482, issued 18 Aug. 1942 to Ambrose, U.S. Pat. No. 2,984,087, issued 16 May 1961 to Folsom, U.S. Pat. No. 3,447,335, issued 3 Jun. 1969 to Ruff et al. and U.S. Pat. No. 3,995,446, issued 7 Dec. 1976 to Eubank. The present invention differs from all of the cited prior art references in the arrangement and function of its dampers.
The space in a building required for installation of a heating and air conditioning system is always a consideration. Designers usually strive to make such systems as compact as possible. The system "footprint" or amount of floor space required is particularly important. The footprint problem is very significant in small structures such as mobile homes. There must be a source of outside air for one of the heat exchangers in an air source air conditioning system. In the typical residential "split" air conditioning system, this is accomplished by locating the condenser in a separate enclosure outside the building. This arrangement has disadvantages, especially in structures like portable buildings and mobile homes.
High temperatures in many locations are accompanied by high humidity. When an air conditioning system is operating in the cooling mode in these locations, condensate forms on the system evaporator. A properly designed system must have means for disposing of this condensate. In cooler weather, when a heat pump is operating in the heating mode, frost can form on the evaporator and adversely effect system performance. A properly designed system must have means for defrosting the evaporator.